package net.borderwars.util;

import java.io.ByteArrayOutputStream;

/**
 * Library of utility methods useful in dealing with converting byte arrays
 * to and from strings of hexadecimal digits.
 *
 * @author Craig R. McClanahan
 */

public final class HexUtil {
    // Code from Ajp11, from Apache's JServ

    // Table for HEX to DEC byte translation
    public static final int[] DEC = {
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            00, 01, 02, 03, 04, 05, 06, 07, 8, 9, -1, -1, -1, -1, -1, -1,
            -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
            -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    };

    /**
     * Convert a String of hexadecimal digits into the corresponding
     * byte array by encoding each two hexadecimal digits as a byte.
     *
     * @param digits Hexadecimal digits representation
     * @throws IllegalArgumentException if an invalid hexadecimal digit
     *                                  is found, or the input string contains an odd number of hexadecimal
     *                                  digits
     */
    public static byte[] convert (String digits) {

        ByteArrayOutputStream baos = new ByteArrayOutputStream ();
        for (int i = 0; i < digits.length (); i += 2) {
            char c1 = digits.charAt (i);
            if ((i + 1) >= digits.length ()) {
                throw new IllegalArgumentException
                        ("Error, odd length string!");
            }
            char c2 = digits.charAt (i + 1);
            byte b = 0;
            if ((c1 >= '0') && (c1 <= '9')) {
                b += ((c1 - '0') * 16);
            }
            else
                if ((c1 >= 'a') && (c1 <= 'f')) {
                    b += ((c1 - 'a' + 10) * 16);
                }
                else
                    if ((c1 >= 'A') && (c1 <= 'F')) {
                        b += ((c1 - 'A' + 10) * 16);
                    }
                    else {
                        throw new IllegalArgumentException
                                ("Bad hex character");
                    }
            if ((c2 >= '0') && (c2 <= '9')) {
                b += (c2 - '0');
            }
            else
                if ((c2 >= 'a') && (c2 <= 'f')) {
                    b += (c2 - 'a' + 10);
                }
                else
                    if ((c2 >= 'A') && (c2 <= 'F')) {
                        b += (c2 - 'A' + 10);
                    }
                    else {
                        throw new IllegalArgumentException
                                ("Bad hex character");
                    }
            baos.write (b);
        }
        return (baos.toByteArray ());

    }

    /**
     * Convert a byte array into a printable format containing a
     * String of hexadecimal digit characters (two per byte).
     *
     * @param bytes Byte array representation
     */
    public static String convert (byte bytes[]) {

        StringBuffer sb = new StringBuffer (bytes.length * 2);
        for (int i = 0; i < bytes.length; i++) {
            sb.append (convertDigit ((int) (bytes[i] >> 4)));
            sb.append (convertDigit ((int) (bytes[i] & 0x0f)));
        }
        return (sb.toString ());

    }

    /**
     * Convert 4 hex digits to an int, and return the number of converted
     * bytes.
     *
     * @param hex Byte array containing exactly four hexadecimal digits
     * @throws IllegalArgumentException if an invalid hexadecimal digit
     *                                  is included
     */
    public static int convert2Int (byte[] hex) {
        // Code from Ajp11, from Apache's JServ

        // assert b.length==4
        // assert valid keys
        int len;
        if (hex.length < 4) {
            return 0;
        }
        if (DEC[hex[0]] < 0) {
            throw new IllegalArgumentException ("Bad hex character");
        }
        len = DEC[hex[0]];
        len = len << 4;
        if (DEC[hex[1]] < 0) {
            throw new IllegalArgumentException ("Bad hex character");
        }
        len += DEC[hex[1]];
        len = len << 4;
        if (DEC[hex[2]] < 0) {
            throw new IllegalArgumentException ("Bad hex character");
        }
        len += DEC[hex[2]];
        len = len << 4;
        if (DEC[hex[3]] < 0) {
            throw new IllegalArgumentException ("Bad hex character");
        }
        len += DEC[hex[3]];
        return len;
    }

    /**
     * [Private] Convert the specified value (0 .. 15) to the corresponding
     * hexadecimal digit.
     *
     * @param value Value to be converted
     */
    private static char convertDigit (int value) {

        value &= 0x0f;
        if (value >= 10) {
            return ((char) (value - 10 + 'a'));
        }
        else {
            return ((char) (value + '0'));
        }

    }

}
